Imitators of the ARDS - Implications for diagnosis and treatment

When confronted with a case of acute respiratory failure severe enough to meet the diagnostic criteria of ALI/ARDS but without a predisposing cause, it is important to consider the alternate diagnoses reviewed above, and to attempt to establish a diagnosis as expediently as possible utilizing BAL with differential counts and, if necessary, the consideration for surgical biopsy. The most common error is that the episode of respiratory failure is incorrectly attributed to an infectious pneumonia and appropriate therapy is either not administered or delayed. Because the literature suggests that a delay of specific therapy for some of these conditions worsens outcome, it seems prudent to administer systemic corticosteroids between 250 mg and 100 mg of IV methylprednisolone for a minimum of 3 days prior to the return of BAL, the microbiologic studies, and/or the surgical biopsy. If the microbiologic studies reveal a potential causative agent, corticosteroids would obviously be discontinued. Some would argue that any diffuse pneumonias that fulfills the ALI/ARDS criteria is ALI/ARDS and should be treated accordingly. A similar debate involved John Murray and Tom Petty in 1975.65-66 Petty was the "lumper" and Murray was the "splitter," citing a difference in survivals for the various predisposing causes of ARDS. Neither author mentioned any of the conditions listed in Table 1, however. We submit that it is appropriate to call these conditions the "imitators" of ALI/ARDS since they may meet the diagnostic criteria of ALI/ARDS but have different therapeutic implications and out-comes.